ArkType

ArkType is a validation library for TypeScript. You describe a data type with TypeScript-like syntax, then use it to check data while your program runs.

ArkType lets you write a type as a string or an object, using syntax that looks like TypeScript. The same definition gives you a validator for runtime data and a type you can use in your code. When a value does not match, ArkType returns messages that say what was expected and what arrived. You can also check at runtime whether one type extends another, the same way TypeScript does at compile time.

• Define types with TypeScript-like string syntax
• Error messages that show expected and actual values
• Editor type errors for mistakes in definitions
• Check whether one type extends another
• Ships an agent skill for coding assistants

TypeScript developers who want runtime checks without keeping a separate schema in sync. It also suits API and form work, where readable error messages help users fix their input. Projects that already rely on TypeScript's type system will find the model familiar.

ArkType is open source under the MIT license and free to use. It is a regular JavaScript library, and basic use needs no plugin or build step. Its docs are also available as Markdown, which helps AI coding tools read the current syntax.